Process for preventing cohesion between acrylonitrile polymer fibers with certain pentanediols



United States Patent PROQESS FGR PREVENTING COHESIGN BETWEEN ACRYLONE PQLYMER FIBERS: WITH CER- TAIN PENIANEDIOLS William M. Blankenship, Waldorf, Md., and James R. Worley, Scaford, Va, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Sept. 22, 1960, Ser. No. 57,625 11 Claims. (Cl. 1177) The present invention contributes to the man-made synthetic textile fiber art. It has reference to improvements in the manufacture of certain varieties of fibers of the type that are based essentially upon acrylonitrile polymers and which are wet spun in and with aqueous saline systems to form intermediate aquagel filamentary structures which, in the final stages of manufacture, are irreversibly dried to provide the desired, characteristically hydrophobic textile fiber product. The present invention relates more particularly to the treatment of such aquagels with specific varieties of opening agents to prevent filamentary bonding, sticking and adhesion during their drying from the highly hydrated aquagel state to their finished textile fiber form.

In the wet spinning of acrylonitrile polymer fibers, it is usually convenient and expedient to form the fibers in continuous or endless filamentary lengths that are assembled in contiguous relationship during their manufacture as multiple filament strands or gatherings. Quite frequently, the filaments are handled during and subsequent to spinning in multiple filament arrays or arrangements in which a considerable plurality of individual, component continuous filaments are in closely associated, substantially or ostensibly parallel relationship. Such tow bundles or like assemblages may oftentimes be of considerable magnitude. It is not unusual, for example, in the manufacture of, say, 1 to denier products, to encounter tow bundles that are comprised of from 10,000 or 50,000 to 200,000 or more individual component endless or continuous filaments.

One of the serious problems encountered when aquagel fibers are being processed in the indicated manner is the tendency of individual filaments to adhere or stick to one another. Such behavior causes coarse, bonded ribbons to be formed which have many undesirable characteristics and which introduce many disadvantages. Fibers that have become so stuck and interwelded to one another generally suffer from a hard hand, lumpy feel, stiffness, lack of luster and other deficiencies tending to cause their quality as textile products to be other than premium.

A major cause of fiber sticking in aquagel filaments is thought to be the high surface tension that exists between the wet surfaces of adjacent filarnents. Such surface tension exerts a considerable bonding force between adjacent fibers. Other causes which contribute to sticking of aquagel filaments are the particular chemical characteristics of a filamentary material being handled which engender or permit welding together of adjacent strands under conditions of close contact, especially under the infiuence of heat at elevated temperatures. Oftentimes the moisture that is present serves as a plasticizer for some of the components in the aquagel yarn so as to occasion a sticking phenomenon in the wet stage processing of the material which would not occur in its handling in a dried condition.

Problems of interfilamentary sticking and bonding commonly occur in spinning, washing and stretching operations during the manufacture of various synthetic fibers produced by diverse wet spinning techniques. Many additives, usually referred to and known as being opening agents, have been employed to prevent the adhesion of individual filaments during processing. In the usual early stages of spinning, washing and stretching, the typical opening agent additives that have been utilized are oil emulsions or surface active materials, or both, which are effective to a greater or lesser extent to prevent interfilamentary welding during fiber to fiber contact in the processing. Agents of this general variety are also sometimes referred to as lubricants.

In the manufacture of wet spun acrylonitrile polymer fibers by the referred-to aquagel process in which aqueous saline solvents are employed, the problems of interfilament adhesion in spinning and stretching stages are not of particular consequence and, prior to final washing before drying of the aquagel yarn, can be handled quite nicely in the conventional manner. With such filaments, however, the sticking and interfilament bonding problem is severe and exceptionally serious during the hot air drying of the intermediate aquagel product to the finally obtained, irreversibly dried, hydrophobic yarn structure. It would be of considerable advantage to provide opening agents which would be satisfactorily effective to prevent interfilamentary bonding and sticking together of individual yarn strands during the irreversibly drying in hot air of acrynonitrile polymer aquagel fibers.

Therefore, it is the principal object of the present invention to provide new and improved opening agents for acrylonitrile polymer aquagel fibers effective upon and for the irreversible drying of such aquagel structures to a characteristically hydrophobic, synthetic textile fiber product.

A further object of the invention is to provide opening agents for acrylonitrile polymer aquagel fibers of the fugitive type or variety which would not remain in or with the yarn to a significant degree after the drying, but would be substantially completely removed therefrom during such operation.

Further objects, and the many advantages and benefits of the present invention, will be manifest in the following description and specification.

The present invention relates to a significant improvement in the process of irreversibly drying an acrylonitrile polymer aquagel fiber, or an aquagel structure based essentially on an acrylonitrile polymer (particularly polyacrylonitrile), to a finally dried, characteristically hydrophobic, synthetic textile fiber form desired. According to the invention, the improvement consists of impregnating a wet spun and washed and, advantageously, stretched (i.e., at least partially, if not completely, oriented) acrylonitrile polymer aquagel fiber prior to its final irreversible drying in hot air with an aqueous solution of a chemical opening agent which consists of a compound, or mixture of compounds, from the class of pentanediols characterized in having the general structure:

wherein R and R are hydrogen or alkyl radicals containing from 1 to about carbon atoms, with the limitation that the sum of the carbon atoms of R and R is at least 2; and, R is hydrogen or an alkyl radical containing from 1 to about 3 carbon atoms.

Advantageously the pentanediol that is employed is 2,2,4-trimethyl-1,3-pentanediol. Other typical species of the pentanediols that may be beneficially utilized in the practice of the present invention are: 2-ethyl-2-methyl- 1,3-pentanediol; 2,2-dipropyl-1,3-pentanediol; 2-amyl-2- methyl-1,3-pentanediol; 2,2-dimethyl 1,3 pentanediol; 2,2-dimethyl-4-ethyl-1,3-pentanediol, etc. Preferable of the pentanediols desirable to use in the invention are those in which R and R are simultaneously the same 1 to 5 carbon atom alkyl radical.

The opening agents utilized in the practice of the present invention generally produce aqueous solutions or suspensions having surface tensions of less than about 50 dynes per square centimeter; are sufiiciently water-insoluble (ranging from only slightly soluble up to about 4 percent based on the weight of the solution) to permit their presence as incompatible oils with the fiber after the initial stages of drying (wherein a major part of the water present is removed) and during the critical finishing drying stage, wherein the majority of sticking and interfilamentary bonding occurs; impart a non-adhesive film to the surface of the acrylonitrile polymer fiber that is treated (even when acrylic alloy fibers are involved, i.e., of the type containing polyvinyllactam adjuvants or other water-soluble or, at least, hydrophilic polymeric ingredients as dye-assistants); and are capable of being efficiently and efiectively removed near the end of the drying under the indicated conditions so as to eliminate the possibility of their chemical reaction with the fiber base and to avoid other undesirable consequences. Such features and characteristics secure for the pentanediols the capability of being quite advantageously utilized as fugitive opening agents in the practice and for the purposes of the present invention. They possibilitate a most satisfactory and beneficial effect.

The pentanediol opening agents of the present invention are applied to the intermediate aquagel fiber (or tow bundles thereof) which has been prepared by wet spinning techniques using aqueous saline solutions to prepare the polymer dissolving spinning solutions as well as the coagulating baths therefor. The opening agent is applied after the aquagel has been washed completely or substantially completely from residual salt and, either concurrently with or subsequent to hot stretching for purposes of orientation of the aquagel fiber product. It is generally most covenient to apply the agent after stretch orientation and to make the application from a flushing bath, wherein the residual moisture or water content in the aquagel fiber is replaced by the applicating solution or dispersion of the pentanediol opening agent. Advantageously, the temperature or the applicating solution is maintained in the range of 2030 C. Of course, as has been indicated, it is most expedient to employ the opening agent on the aquagel fibers in tow bundle form.

Thus, for purposes of further particularization, the opening agents of the present invention are applied to strandular, filamentary and the like aquagel structural forms of fiber-forming polymers that are based upon acrylonitrile. These hydrated forms of the polymer, as is well known, may be obtained by extruding a spinning solution of the polymer into an aqueous coagulating bath wherein the spinning solvent in the extruded filamentary structure is replaced to a large extent with water. Such water swollen or hydrated filamentary structures, as has been indicated in the foregoing, can advantageously be prepared by extruding solutions or other spinnable dispersions of the fiber-forming acrylonitrile polymers in polyacrylonitrile-dissolving aqueous saline solvents into aqueous, non-polymer-dissolving coagulating spin bath solutions of the same salt or salts as used in the spinning solution. Advantageously, zinc chloride or its saline equivalents for such purpose are utilized, including such salts as calcium and other thiocyanates (as disclosed in US. Patents Nos. 2,140,921 and 2,425,192), lithium bromide, salts of the so-called lyotropic series (as disclosed in US. Patents Nos. 2,648,592; 2,648,593; 2,648,646; 2,648,648 and 2,648,649), and saline equivalents thereof. Although it is desirable for the amount of Water that is in the aquagel to at least gravimetrically equal the hydrated polymer that is contained therein, it may oftentimes be preferable for the water to polymer Weight ratio in the aquagel to be in the neighborhood of from about 1.521 to 2.0: 1, respectively. Aquagel structures in which the water to polymer ratio is as high as 2.5 or 3:1 and higher may also be satisfactorily employed.

The aquagel fibers that are treated with the pentanediol opening agents in the practice of the present invention which are based essentially on fiber-forming acrylonitrile polymers may be the usual homopolymer or copolymer compositions containing in the polymer molecule at least about percent by weight of acrylonitrile that are adapted to provide the variety of filamentary products that are conveniently referred to as being acrylic fibers. Illustrative examples of monomers that may be copolymerized with acrylonitrile to form the above-mentioned copolymers are compounds containing a single vinyl (CH =C grouping, for instance vinyl esters of monocarboxylic acids, e.g., vinyl acetate, vinyl propionate, etc.; acrylic acid, methacrylic acid, etc., and esters and amides of such acids, e.g., methyl, ethyl, and propyl acrylates and methacrylates, acrylamide, methacrylamide, N-alkyl acrylamides, e.g., N-rnethyl, N-ethyl, etc.; vinyl sulfonic acids; vinyl substituted aromatic sulfonic acids; vinyl pyridines; and other of the ethylenically unsaturated monomers copolymerizable with acrylonitrile to form fiber-forming copolymers.

Or, the basic acrylonitrile polymer composition may contain or have other beneficial additament ingredients incorporated or combined therein. These may be the typical pigments, delusterants, textile assistants and the like (including antistatic agents) or they may be dyeassisting adjuvant materials. Thus, minor proportions (generally less than about 20 percent and frequently be tween about 1 and 15 percent, of the dry weight of the fiber) of certain dye-receptive polymers may be incorporated in a polyacrylonitrile or other acrylonitrile aquagel fiber that is treated in accordance with the present invention. The dye-receptive polymers may be vinyl lactam polymers, including poly-N-vinyl-2-pyrro1idone, poly- N-vinyl-Z-caprolactam, and the like; N-vinyl-2-oxazolidinone polymers, including poly-N-vinyl-2-oxazolidinone, poly-N-vinyl-S-methyl-2-oxazolidinone and the like; poly- N-vinyl-3-morpholinone and the like; and more or less equivalent polymeric dye-assistant adjuvants. The dyeassisting adjuvant materials of acrylic alloy type fibers may also be present in the essential acrylonitrile polymer base in the form of graft or block copolymerized units of such polymers upon an already formed acrylonitrile polymer base or, alternatively, polymeric products in which the essential acrylonitrile polymer base is graft or block copolymerized on an already formed dye-assisting adjuvant polymer backbone. It is generally preferred, for purposes of terminological classification, to characterize the latter, highly advantageous variety of dye-receptive fibers as being acrylic alloy fibers in order to clearly distinguish them from the conventional, prototype, socalled acrylic fibers that were first known to the art.

The application path of the pentanediol opening agent may be either a Water solution or colloidal suspension thereof containing from about 0.1 to about 4 percent, and preferably at least about 0.5 percent, of dispersed active agent. It is generally desirable for the pentanediol opening agents to be formulated in the applicating compositions thereof as near saturated solutions, i.e., in aqueous dispersions wherein their concentration is not in excess of that at which they form true solutions or colloidal suspensions. Such manner of employment beneficially avoids the deposition of large oily particles on the aquagel fibers being treated, which might tend to produce nonuniform effects in the treatment. Advantageously, the bath imparts between about 0.75 to 6 percent and preferably between about 1 and 3 percent by weight on the Weight of the dry fiber (owf.) of the opening agent on the aquagel fiber. While it is advantageous to apply the opening agent from an impregnating bath, suitable results may also be achieved by spraying, rolling or wiping (as with wick applicators) the applicating solution of the opening agent on the aquegel fibers being treated.

It is generally advantageous to apply the opening agents to the aquagel fibers or tow bundles thereof prior to any wet-crimping operation that may be contemplated for the fibers, if and when such operation isincluded in the processing sequence. Following the application of the opening agent, the aquagel fibers are irreversibly dried, to provide the desired, characteristically hydrophobic, synthetic textile fiber product. Drying is best accomplished in and with hot air at temperatures between about 100 and 150 C. for periods of time between about 30 and 5 minutes. Fibers treated and dried in accordance with the present invention may generally be obtained in excellent finished form. They have substantially, if not completely, reduced occurrence of undesired sticking and interfilamentary bonding and are in a condition wherein the optimum properties of the fiber product is brought out to best advantage.

One peculiar and distinctively beneficial advantage of the pentanediol opening agents that are employed in the practice of the present invention lies in their ability to be successfully and satisfactorily recovered for re-use after their application in the process. As is evident in the foregoing, the aquagel tow bundle entering the drying oven or chamber can be shown to contain the agent. However, the irreversibly dried dried fiber product leaving the drying area contains none or vanishingly small and insignificant quantities of the agent. This is experienced despite the fact that successful opening action has been accomplished and the agent has operated in the desired manner during the drying step. It is believed that the agent is removed from the aquagel structure being dried by means of steam distillation. Thus, recovery of the condensate and re-use of the agent is an attractive feature of the present invention. Of at least as great importance is the fact that, due to the fugitive and non-residual character of the pentanediol opening agents, they are absent from the finally dried fiber, thus avoiding any possibility for interfering with subsequent processing operations and normal usage of the textile product. In this way, fibers prepared following the practice of the present invention experience no decrease in heat or light stability, luster or dyeability. They have a completely dry and non-oily hand, and are not subject to being tacky or otherwise altered due to the presence of residual opening agent on their surfaces.

The fiow diagram in the drawing represents the process steps in which the acrylonitrile polymer fiber is treated with pentanediol.

The invention is further illustrated in and by the following examples wherein, unless otherwise indicated, all parts and percentages are to be taken by weight.

EXAMPLE 1 A polyacrylonitrile spinning solution was prepared by dissolving about one part of a fiber-forming species of the polymer having an average molecular weight between about 30 and 35 thousand in about parts of a 60 percent aqueous solution of zinc chloride. The spinning solution had a viscosity of about 2200 poises at a temperature of about C. -It is extruded at about C. through a spinnerette system into about three hundred separate, individual aquagel filaments. The diameter of each jet hole through which each individual filament was extruded was about 15 mils. The extruded spinning solution was coagulated in a coagulating liquid comprised of about a 43 percent aqueous solution of zinc chloride at 15 C. The aquasgel filaments were withdrawn from the coagulating liquid and assembled in the form of a relatively flat, ribbon-like, multiple filament tow bundle. The wet spun tow was then passed into a water wash bath, wherein it was washed to the point at which the zinc chloride content was not in excess of about 0.05 percent. The washed tow was then oriented by being stretched to a total length of about 12 times its original length. By these operations there was obtained a washed and oriented filamentary tow bundle Off the 300 individual aquazgel strands. The total aquagel denier of the washed and oriented tow bundle was about 5400. The oriented aquagel structures contained about 2.0 parts of water for each part of fiber-forming polyacrylonitrile that was present therein. In addition, the aquagel contained about 7 percent of poly-N-vinyl-2-pyrrolidone (PVP) (based on the dry weight fiber) that had been incorporated therein as \a polymeric dye-assisting adjuvant by impregnation of the water-soluble polymer (from an impregnating bath in which it was contained in aqueous solution) into the aquagel structure.

The washed and oriented tow was then passed in a relaxed state onto a continuous belt drier and dried in hot air at C. for about 18 minutes to achieve the ineversible drying and convert the aquagel to the final characteristically hydrophobic, synthetic textile fiber structure. The tow bundle (designated as sample A) was then tested by a standard method of analysis to deermine the number of sticks in the finally obtained product. The analysis method employed is one common and well known to the art, wherein a card web of the fiber is observed in order to count neps or blemishes therein. A segment of carded web fiber is visually examined after a specified running time through laboratory Neptometcr which simulates a sample card. Sticks are an expression of the number of bonded fibers observed on a standard sample. A one-minute running time through the sample card (Neptometer) is found to approximate the standard cotton carding operation performed on a production scale. The sticks observed after such treatment provide an accurate picture or representation of the frequency or number of bonded fibers present.

In contrast with the foregoing, the spinning and drying procedure was repeated on additional tow bundle samples excepting that, immediately prior to drying the washed and stretched tow bundles, they were passed through an aqueous appl-icating solution of a pentane-diol opening agent, or, through an applicating solution of a polyol not included in the present invention, in accordance with the practice of the present invention at room temperature with about a two second residence (immersion) time of each tow bundle sample in the bath.

The treated samples were nun through the sample card according to the procedure described for the untreated control sample (sample A). The samples were then objectively rated for openness according to the number of sticks in the standard sample card web and assigned numbers from 0 to 5 to compare the relative improvements between samples. The lower the number assigned to the sample the better the openness of the web or the fewer the sticks in the sample. For instance, a sample assigned a zero (0) rating will usually be essentially void of any sticks, and a sample assigned a four (4) rating will usually have as a minimum about 40 sticks per gram.

In addition to rating the samples by sticks, they were also rated as to feel, that is, softness of hand-the lower the rating number the softer or less harsh was the sample. The samples were also rated according to whitenessthe lower rating numbers indicating the whiter samples. The results are set forth in the following tabulation.

Table Concentration, Rating after 1 minute cording Percent by on laboratory N eptometer Sample Agent Applied Weight in Applicattng Solution Openness Feel Whitencss Water (no agent) 4 4 4 2,4- rimetl1yl-1,3-pontanodi0l. 1. 96 1 1-2 -1 1. 74 1 1-2 0-1 1. 1S 2 2 0-1 0. 79' 3 3 0-1 2,Q-(liethyl-1,3pentanedi0l 1. 96 2 2 0-1 2,2-dimethyl-1,3-pentauediol 1. Q6 3 3 0-1 2ethyl-4-propyl-l,3

pentanediol. 1. 96 4 4 0-1 2,4-pentanedi0l 1. 96 4 1 3 1,2,6-hexanetrioL 1. 96 5 5 5 Ethylene glycol. 1. 96 5 5 5 EXAMPLE 2 An aquagel tow bundle is prepared identically as in Example 1 with the major exception that no PVP is incorporated in the polyacrylon'itrile fibers. The tow bundle, prior to drying, is treated with 2,2,4-tnimethyl- 1,3-pentanediol in the same way as sample B in the first example. The dried, treated tow bundle is exceptionally open and fluffy. Its individual component filaments are distinctly individual and non-bonded. in marked contrast therewith, an identical polyacrylonitrile aquagel tow bundle that is dried without being treated in accordance with the present invention has a significantly inferior and undesirable shredded whea fibrous appearance and reel.

EXAMPLE 3 Similar results are obtained when the foregoing is repeated excepting to use other forms and types of unmodified polyacrylonitrile or to employ unmodified acrylonitrile copolymer fibers or when using acrylic alloy fibers containing other polymeric dye-assisting adjuvants in place of the poly-N-vinyl-2-pyrrolidone, such as poly- N-vinyl-Z-oxazolidinone, poly-N-vinyl-S-methyl 2 oxazolidinone, poly-N-vinyl-3 morpholinone, etc. Analogous excellent results are also obtained when using other 0d: the pentanediols as the opening agent that have been specifically described herein or fitting within the scope of Formula I.

The scope and purview of the invention is to be gauged in the light of the hereto appended claims rather than strictly from the docent embodiments that have been set forth in the foregoing description and specification.

What is claimed is:

1. In the method of irreversibly drying a salt spun acrylonitrile polymer aquagel fiber to convert it to a syn thetic, characteristically hydrophobic, textile fiber product, said aquagel consisting essentially of an ethylenically unsaturated monomeric material containing at least about 80 weight percent polymerized acrylonitrile, said aquagel having been Washed essentially free of any residual salt and containing between about 1 and 3 parts by weight of hydrated water to each part of dry polymer therein and having been at least partially oriented, the improvement which consists of applying from an aqueous dispersion to said aqnagel fiber prior to drying between about 0.75 to 6 percent based on the weight of the aquage-l fiber, of a pentanediol opening agent selected from the class consisting of those having the structural formula:-

wherein R and R are hydrogen or alkyl radicals containing from 1 to about 5 carbon atoms, with the limitation that the sum of the carbon atoms of R and R is at least 2; and, R is hydrogen or an alkyl radical containing from 1 to about 3 carbon atoms; then irreversibly drying the aquagel in hot air at a temperature between about and C. for a period of time between about 30 and 5 minutes.

2. The method of claim 1, wherein said opening agent is applied to said aquagel fiber from an applicating aqueous bath of said agent containing between about 0.1 and 4 percent by weight, based on the weight of the bath, of said opening agent dispersed therein.

3. The method of claim 2, wherein opening agent is applied by immersing said fiber in said applicating bath.

4. The method of claim 1, wherein said aquagel fiber is treated and dried while it is assembled in tow bundle form.

5. The method of claim 1, wherein said aquagel fiber is a polyaory-lonitrile fiber.

6. The method of claim 1, wherein said aquagel fiber is an acrylic alloy fiber which consists essentially of a composition of (1) at least about 80 weight percent, based on the dry weight of the composition, of an ethylenically unsaturated monomeric material containing at least about 80 weight percent \Olf polymerized acrylonitrile, and (2) up to about 20 weight percent, based on the dry weight of the composition, of a polymerized dyeassisting adjuvant selected from the group consisting of polymerized N-vinyl-2-pyrrolidone, polymerized N-vinyl- Z-caprolactam, polymerized N vinyl 2 oxazolidinone, polymerized N-vinyl-5- nethyl-2=oxazolidinone and polymerized l-lvinyl-3-morpholinone.

7. The method of claim 6, wherein said acrylic al- 10y fiber is comprised of polyacrylonitrile containing intimately blended therewith up to about 20 percent .by weight, based on the dry weight or the fiber, of poly-N- vinyl-2-pyrrolidone as a dye-assisting adjuv-ant.

8. The method of claim 1, wherein said opening agent is 2,2,4-trimethyl-1,3-pentanediol.

9. The method of claim 1, wherein said opening agent is 2,2-diethyl-1,3-pentanediol.

10. The method or" claim 1, wherein said opening agent is 2,2-dime-thyl-1,3-pentanediol.

11. The method of claim 1, wherein R and R in Formula I are simultaneously the same 1 to 5 carbon atom alkyl radical.

References (Iited in the file of this patent UNITED STATES PATENTS 2,558,735 Cresswell July 3, 1951 2,615,002 Hurwitz Oct. 21, 1952 FOREIGN PATENTS 652,557 Great Britain Apr. 25, 1951 OTHER REFERENCES Synthetic Ester Lubricants, by Barnes et al., Lubrication Engineering, August 1957. 

1. IN THE METHOD OF IRREVERSIBLY DRYING A SALT SPUN ACRYLONITRILE POLYMER AQUAGEL FIBER TO CONVERT IT TO A SYNTHETIC, CHARACTERISTICALLY HYDROPHOBIC, TEXTILE FIBER PRODUCT, SAID AQUAGEL CONSISTING ESSENTIALLY OF AN ETHYLENICALLY UNSATURATED MONOMERIC MATERIAL CONTAINING AT LEAST ABOUT 80 WEIGHT PERCENT POLYMERIZED ACRYLONITRILE, SAID AQUAGEL HAVING BEEN WASHED ESSENTIALLY FREE OF ANY RESIDUAL SALT AND CONTAINING BETWEEN ABOUT 1 AND 3 PARTS BY WEIGHT OF HYDRATED WATER TO EACH PART OF DRY POLYMER THEREIN AND HAVING BEEN AT LEAST PARTIALLY ORIENTED, THE IMPROVEMENT WHICH CONSISTS OF APPLYING FROM AN AQUEOUS DISPERSION TO SAID AQUAGEL FIBER PRIOR TO DRYING BETWEEN ABOUT 0.75 TO 6 PERCENT BASED ON THE WEIGHT OF THE AQUAGEL FIBER, OF A PENTANEDIOL OPENING AGENT SELECTED FROM THE CLASS CONSISTING OF THOSE HAVING THE STRUCTURAL FORMULA: 